Ultra-high temperature carbide foams and methods of fabricating the same

ABSTRACT

Ultra-high temperature carbide (UHTC) foams and methods of fabricating and using the same are provided. The UHTC foams are produced in a three-step process, including UHTC slurry preparation, freeze-drying, and spark plasma sintering (SPS). The fabrication methods allow for the production of any kind of single- or multi-component UHTC foam, while also providing flexibility in the shape and size of the UHTC foams to produce near-net-shape components.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S.application Ser. No. 17/457,778, filed Dec. 6, 2021, the disclosure ofwhich is hereby incorporated by reference in its entirety, including allfigures, tables, and drawings.

GOVERNMENT SUPPORT

This invention was made with government support under DE-NA0003865awarded by the Department of Energy. The government has certain rightsin the invention.

BACKGROUND

Ultra-high temperature carbide (UHTC) ceramics are known for excellentstability at temperatures of at least 2000° C. These materials are alsorecognized as potential useful for thermal protection systems (TPS) dueto capabilities beyond those of existing structural materials. However,bulk UHTCs intrinsically have very high lattice thermal conductivity,which limits their usefulness in the field of thermal insulation. Whenmanaging ultra-high thermal systems, thermal damages can be prevented orinhibited by materials that can either effectively dissipate heat (owingto high thermal conductivity, such as UHTCs) or provide thermalinsulation (owing to low thermal conductivity). UHTC development isprimarily focused on obtaining dense UHTCs.

BRIEF SUMMARY

Embodiments of the subject invention provide novel and advantageousultra-high temperature carbide (UHTC) foams and methods of fabricatingand using the same. The UHTC foams are crack-resistant and have lowthermal conductivity, making them ideal for applications such as thermalinsulation systems, filtration of high-temperature corrosive gases,catalyst support, and high-temperature solar absorptions. The UHTC foamsare produced in a three-step process, including UHTC slurry preparation,freeze-drying, and spark plasma sintering (SPS). The fabrication methodsallow for the production of any kind of single- or multi-component UHTCfoam, while also providing flexibility in the shape and size of the UHTCfoams to produce near-net-shape components.

In an embodiment, a method of fabricating a UHTC foam can comprise:preparing a UHTC slurry; freeze-drying the UHTC slurry to provide agreen body; and performing an SPS process on the green body to providethe UHTC foam; the performing of the SPS process comprising disposingthe green body such that punches of an SPS setup used for the SPSprocess do not touch (or make any physical contact with) the green bodyduring the SPS process, the SPS process thereby being a pressure-lessSPS process. The UHTC foam can be, for example, a tantalum carbide (TaC)foam, a hafnium carbide (HfC) foam, or a foam comprising TaC and HfC(e.g., at a ratio of for example 1:1 (TaC:HfC)). The foam comprising TaCand HfC can be, for example, a solid solution of TaC and HfC (e.g., at aratio of for example 1:1 (TaC:HfC)). The preparing of the UHTC slurrycan comprise: mixing UHTCs in a solvent (e.g., water, such as deionizedwater (e.g., deionized water with no additives)) to form a first slurry,a loading of UHTCs in the first slurry being at least 5 wt % (e.g., atleast 10 wt %, about 10 wt %, or 10 wt %); adding a dispersant (e.g.,polyacrylic acid (PAA)) to the first slurry to obtain a second slurry;and stirring the second slurry to obtain the UHTC slurry. The stirringof the second slurry can comprise stirring the second slurry at a firsttemperature for a first amount of time to maintain a pH of the secondslurry constant (for example, the first temperature can room temperatureand/or the first amount of time can be 5 hours or about 5 hours). Thefreeze-drying of the UHTC slurry can comprise: pouring the UHTC slurryinto a container (e.g., a graphite crucible); and freezing and thensubliming the UHTC slurry in the container to obtain the green body. Thefreeze-drying process can be performed for, e.g., 24 hours or about 24hours. The performing of the SPS process can comprise: providing thegreen body in a container (e.g., the same container used forfreeze-drying; for example, a graphite crucible); disposing thecontainer with the green body in a die (e.g., a graphite die); andperforming the SPS process on the green body in the container in the dieat a second temperature for a second amount of time (for example, thesecond temperature can be 1850° C. or about 1850° C. and/or the secondamount of time can be less than 30 minutes (e.g., less than 20 minutes,about 10 minutes, 10 minutes, or less than 10 minutes)). As mentioned,the entire SPS process can be performed and completed in less than 30minutes (e.g., less than 20 minutes, about 10 minutes, 10 minutes, orless than 10 minutes).

In another embodiment, a UHTC foam can comprise macro-pores, meso-pores,and micro-pores, with a porosity of at least 30% (e.g., at least 40%, atleast 45%, at least 48%, at least 50%, at least 54%, or at least 55%).The UHTC foam can have a thermal conductivity of less than 60 Watts permeter per Kelvin (W/m-K) (e.g., less than 50 W/m-K, less than 45 W/m-K,less than 40 W/m-K, less than 30 W/m-K, less than 25 W/m-K, less than 20W/m-K, less than 15 W/m-K, or less than 10 W/m-K). The UHTC foam can be,for example, a TaC foam, a HfC foam, or a foam comprising TaC and HfC(e.g., at a ratio of for example 1:1 (TaC:HfC)). The foam comprising TaCand HfC can be, for example, a solid solution of TaC and HfC (e.g., at aratio of for example 1:1 (TaC:HfC)).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a step-wise fabrication process for ultra-high temperaturecarbide (UHTC) foams, according to an embodiment of the subjectinvention. First, an aqueous slurry of UHTCs (e.g., with 10 wt % loadingor about 10 wt % loading) can be prepared. A dispersant (e.g.,polyacryclic acid (PAA)) with a loading of UHTC (e.g., 6 wt % or about 6wt % of UHTC loading) can be added to obtain well-dissolved UHTC slurry.The solution/slurry can be stirred (e.g., constantly stirred at a settemperature for a set amount of time (e.g., room temperature for 5 hours(h) or about 5 h)) while maintaining the pH constant or fairly constant(e.g., constant at pH=8 or about 8) throughout the process. The solutioncan then be poured into a mold (e.g., a graphite mold such as a graphitecrucible) and freeze dried (e.g., for a set amount of time such as 24 hor about 24 h). The mold can then be put inside a die (e.g., a sparkplasma sintering (SPS) die) in such a way that the green body remainsuntouched by the two punches (e.g., graphite punches) in order to dopressure-less sintering. Though FIG. 1 lists graphite as the materialfor the die, crucible, and punch, this is for exemplary purposes only;also, though FIG. 1 lists dimensions (12.7 millimeters (mm) in diameterand 12 mm in height) for the fabricated UHTC foam, this is for exemplarypurposes only and should not be construed as limiting.

FIG. 2(a) shows an image of a fabricated UHTC foam for tantalum carbide(TaC). Though FIG. 2(a) lists dimensions (12.7 mm in diameter and 12 mmin height) for the fabricated UHTC foam, this is for exemplary purposesonly and should not be construed as limiting.

FIG. 2(b) shows an image of a fabricated UHTC foam for hafnium carbide(HfC). Though FIG. 2(b) lists dimensions (12.7 mm in diameter and 8 mmin height) for the fabricated UHTC foam, this is for exemplary purposesonly and should not be construed as limiting.

FIG. 2(c) shows an image of a fabricated UHTC foam for TaC and HfC(TaC-HfC). Though FIG. 2(c) lists dimensions (12.7 mm in diameter and 5mm in height) for the fabricated UHTC foam, this is for exemplarypurposes only and should not be construed as limiting.

FIG. 3(a) shows a scanning electron microscope (SEM) image for TaC foam,showing uniform distribution of macro-pores. The scale bar is 500micrometers (μm).

FIG. 3(b) shows an SEM image for TaC foam, showing densified struts andaligned macro-pores. The scale bar is 50 μm.

FIG. 3(c) shows an SEM image of the identified square in FIG. 3(b),showing partially sintered struts and meso-pores in the TaC foam. Thescale bar is 10 μm.

FIG. 3(d) shows an SEM image of the identified square in FIG. 3(c),showing micro-pores in struts in the TaC foam. The scale bar is 1 μm.

FIG. 4(a) shows an SEM image for HfC foam, showing uniform distributionof macro-pores. The scale bar is 500 μm.

FIG. 4(b) shows an SEM image for HfC foam, showing densified regions,macro-pores, and meso-pores. The scale bar is 50 μm.

FIG. 4(c) shows an SEM image of the identified square in FIG. 4(b),showing partially sintered struts in the HfC foam. The scale bar is 10μm.

FIG. 4(d) shows an SEM image of the identified square in FIG. 4(c),showing micro-pores and pore closure in the HfC foam. The scale bar is 1μm.

FIG. 5(a) shows an SEM image for TaC-HfC foam, showing uniformdistribution of macro-pores. The scale bar is 500 μm.

FIG. 5(b) shows an SEM image for TaC-HfC foam. The scale bar is 50 μm.

FIG. 5(c) shows an SEM image of the identified square in FIG. 5(b),showing struts in the TaC-HfC foam. The scale bar is 10 μm.

FIG. 5(d) shows an SEM image of the identified square in FIG. 5(c),showing uniform distribution of micro-pores in the TaC-HfC foam. Thescale bar is 1 μm.

FIG. 6 shows an area selected for energy dispersive spectroscopy (EDS)mapping in TaC-HfC foam. The scale bar is 100 μm.

FIG. 7 shows EDS mapping for the carbon (C) in the TaC-HfC foam fromFIG. 6 . The scale bar is 100 μm.

FIG. 8 shows EDS mapping for the Hf in the TaC-HfC foam from FIG. 6 .The scale bar is 100 μm.

FIG. 9 shows EDS mapping for the Ta in the TaC-HfC foam from FIG. 6 .The scale bar is 100 μm.

FIG. 10 shows the intensity (counts) versus energy (in kilo-electronVolts (keV)) for the EDS mapping for the TaC-HfC foam, showing uniformsolid-solution formation in the foam from FIG. 6 .

FIG. 11 shows a comparison of X-ray diffraction (XRD) spectra of freezedried TaC-HfC UHTC foam (labeled “FD_TaC-HfC” in FIG. 11 ) andpressure-less SPS TaC-HfC UHTCs (labeled “SPS_TaC-HfC” in FIG. 11 ). Thepartial solid solutioning was observed in TaC-HfC foam after sintering.

FIG. 12 shows a plot of load (in Newtons (N)) versus displacement (inmm) for showing position control high load indentation, showing themechanical integrity (along with load bearing capabilities) for TaCfoam. Indentations were carried out using a spherical tip (R=about 3 mm)at a rate of 0.1 millimeters per minute (mm/min) up to 20% of itsinitial height using a 4000 N capacity load cell. The corresponding loadin the sample obtained relates to the load bearing capacity of thesample. The kinks in the curve correspond to the events such as porosityencounter, crack initiation, crack propagation, and failure in the foam.The TaC foam did not break during testing.

FIG. 13 shows a plot of load (in N) versus displacement (in mm) forshowing position control high load indentation, showing the mechanicalintegrity (along with load bearing capabilities) for HfC foam. Thetesting was carried out as described for FIG. 12 . The HfC foam did notbreak during testing.

FIG. 14 shows a plot of load (in N) versus displacement (in mm) forshowing position control high load indentation, showing the mechanicalintegrity (along with load bearing capabilities) for TaC-HfC foam. Thetesting was carried out as described for FIG. 12 . The TaC-HfC foam didnot break during testing.

FIG. 15 shows a plot of thermal conductivity (in Watts per meter perKelvin (W/m-K)) versus temperature (in ° C.) for TaC, HfC, and TaC-HfCUHTC foams. The curve with the highest thermal conductivity values (withthe square data points) is for the TaC foam; the curve with thesecond-highest conductivity values (with the circle data points) is forthe HfC foam; and the curve with the lowest conductivity values (withthe triangle data points) is for the TaC-HfC foam.

DETAILED DESCRIPTION

Embodiments of the subject invention provide novel and advantageousultra-high temperature carbide (UHTC) foams and methods of fabricatingand using the same. The UHTC foams are crack-resistant and have lowthermal conductivity, making them ideal for applications such as thermalinsulation systems, filtration of high-temperature corrosive gases,catalyst support, and high-temperature solar absorptions. The UHTC foamsare produced in a three-step process, including UHTC slurry preparation,freeze-drying, and spark plasma sintering (SPS). The fabrication methodsallow for the production of any kind of single- or multi-component UHTCfoam, while also providing flexibility in the shape and size of the UHTCfoams to produce near-net-shape components. It is noted that a UHTCmaterial is defined as showing good stability at a temperature of atleast 2000° C.

Contrary to existing UHTC ceramics, the development of which is focusedon dense UHTCs, embodiments of the subject invention can provide porousUHTC foams. The porosity in the UHTC is not a defect, but rather afunctional property tailored specifically for the final application(e.g., thermal insulation systems, filtration of high-temperaturecorrosive gases, catalyst support, and/or high-temperature solarabsorptions). These UHTC foams provide an advantageous combination ofproperties of low overall weight and low thermal conductivity. Thissolves the concerns related to the durability of UHTCs and, combinedwith the other advantages of these UHTC foams of embodiments of thesubject invention, can end up saving huge amounts of money per pound ofpayload-to-orbit for rockets.

Prior to the UHTC foams of embodiments of the subject invention, thedevelopment of foams of high-temperature materials involved replicationmethods, direct foaming methods, precursor infiltration and pyrolysis,and chemical vapor deposition (CVD). Due to high covalent bonding andlow self-diffusion coefficients, sintering of UHTC foams is challenging.Prolonged sintering time and high sintering temperature cansignificantly affect the pore size, inter-connecting structure, anddensity of the foams. Moderate sintering temperature can affect the handability of the UHTC foams. Hence, the currently available related artmethods that could be used to fabricate UHTC foams are time-consuming,expensive, and/or result in foams with poor mechanical strength.

Embodiments of the subject invention provide novel foam-gel,casting-freeze-drying (FD) technology to fabricate bulk porous UHTCs. Asa field-assisted sintering technique, SPS is known to obtain porousmaterials by partial or controlled densification. In embodiments of thesubject invention, the SPS process can be calibrated to be used as apressure-less technique. The usage of SPS as a pressure-less techniquecan be divided into: (i) retarded grain growth for enhanced mechanicalstrength; (ii) retaining the porous structure obtained during FD withcontrolled pore-shape, pore-size, and/or interconnection; and (iii)consolidation in a short time. Thus, the calibrated SPS of the porousgreen body of UHTCs maintains the ultra-high porosity of UHTCs havinglow thermal conductivity and high strength. This technique applies toall high-temperature ceramic classes, including UHTCs and high-entropyUHTCs (HE-UHTCs).

The microstructure properties of foams are strongly dependent on thepreparation protocols. Partial sintering is the most straightforwardroute for fabricating porous ceramics, but this method usually resultsin either lower porosity or lower strength foams. Ceramic foams withhigh porosity are typically prepared by a replica, sacrificial template,and direct foaming method, in which pre-ceramic polymers are involved.All of these methods have only been applied to oxides and silicon-basednon-ceramic foams.

In many embodiments of the subject invention, no hazardoussurfactants/dispersants are used. The liquid medium for UHTC dispersioncan be, for example, water (e.g., deionized water, such as deionizedwater with no additives), and the dispersant for UHTC dispersion can be,for example, polyacrylic acid (PAA). Embodiments therefore provide aninexpensive, non-toxic, environmentally-friendly way to prepare UHTCslurries. The dispersion of the UHTC can be done by stirring thesolution while maintaining a pH of 8 (or about 8). This mixing processis controllable, facile, and can be easily scaled up from laboratoryscale to industry scale. The unique combination of FD and calibrated SPStechniques offers an attractive combination of properties of low overallweight, low thermal conductivity, and high mechanical strength for thefabricated UHTC foams. The methods of embodiments of the subjectinvention provide flexibility in the shape and size of the UHTC foams,allowing for production of near-net-shape components.

FIG. 1 shows a step-wise fabrication method for ultra-high temperaturecarbide (UHTC) foams, according to an embodiment of the subjectinvention. The method can include UHTC slurry preparation, freezedrying, and SPS.

First, an aqueous slurry of UHTCs (e.g., with 10 wt % loading or about10 wt % loading) can be prepared. A dispersant (e.g., PAA) with aloading of UHTC (e.g., 6 wt % or about 6 wt % of UHTC loading) can beadded to obtain well-dissolved UHTC slurry. The solution/slurry can bestirred (e.g., constantly stirred at a set temperature for a set amountof time (e.g., room temperature for 5 hours (h) or about 5 h)) whilemaintaining the pH constant or fairly constant (e.g., constant at pH=8or about 8) throughout the process. By maintaining the pH, a polymerratio to UHTC carbide loading is controllable to obtain repeatable andscalable production methods.

The solution/slurry can then be poured into a mold (e.g., a graphitemold such as a graphite crucible) and freeze dried (e.g., for a setamount of time such as 24 h or about 24 h) to obtain a green body. Thefreeze drying can include the slurry being frozen and then subsequentlysublimed in a freeze drying (e.g., for a set amount of time such as 24 hor about 24 h) to obtain the green body. The use of the freeze dryingtechnique on UHTCs is performed here for the first time on monolithicUHTCs (e.g., TaC, HfC) and a binary composite (e.g., TaC-HfC).

The green body obtained from the FD technique can be sintered bycalibrating a conventional SPS setup. The green body can be kept insidea container (e.g., a graphite container and/or a crucible, such as agraphite crucible). The whole assembly, including the green body and thecontainer, can be put inside a die (e.g., a graphite die). In themodified punch design, the working space can remain constant between thepunches of the SPS setup by not touching the green body sample insidethe die (e.g., a standard graphite die), resulting in zero externalpressure. The SPS parameters can be configured for pressure-lesssintering (e.g., at a set temperature for a set amount of time, such asat 1850° C. or about 1850° C. for 10 minutes (min) or about 10 min).After the pressure-less SPS, the final UHTC foam is obtained (see, e.g.,FIGS. 2(a), 2(b), 2(c), and the bottom-right corner of FIG. 1 ).

The thermal insulation properties of the UHTC foam can be altered byadjusting the kinetics (during SPS processing), which regulates themutual solubility in two/multi-component UHTCs. For example, partialsolid-solution formation in a two-component UHTC (TaC-HfC) system with asintering time of 10 mins has been shown (see, e.g., Example 1). Thetailoring of the thermal insulation can be further done by adding morecomponents in a UHTC system while maintaining the same mechanicalintegrity or improving the mechanical integrity. The methods ofembodiments of the subject invention can also be used to make UHTC foamsof desired shape and size.

Embodiments of the subject invention provide a practical approach toultra-light, strong UHTCs for thermal insulation. Ultra-high porosityand low sintering shrinkage are attributed to the fact that thefreeze-drying technique reduces surface tension and UHTC particles havevery low self-diffusion during sintering. Also, the shorter dwellingtime during SPS (e.g., less than 30 min, such as 10 min or about 10 min)preserves the FD porous structure while achieving high mechanicalstrength.

UHTC foams of embodiments of the subject invention can be used invarious engineering applications, including in the energy and aerospacesectors. Applications of the UHTC foams can include high-temperaturethermal insulation, support membrane for catalysis, hot/corrosive gasinfiltration, high-temperature solar absorption, concentrated solarpower (CSP), solar receivers, thermo-electric conversion, hypersonicvehicles, atmospheric entry probes, radiant burners, gas and/or chemicalsensors, insulator panels, and thrust chambers and/or rocket nozzles ina space propulsion system.

The transitional term “comprising,” “comprises,” or “comprise” isinclusive or open-ended and does not exclude additional, unrecitedelements or method steps. By contrast, the transitional phrase“consisting of” excludes any element, step, or ingredient not specifiedin the claim. The phrases “consisting” or “consists essentially of”indicate that the claim encompasses embodiments containing the specifiedmaterials or steps and those that do not materially affect the basic andnovel characteristic(s) of the claim. Use of the term “comprising”contemplates other embodiments that “consist” or “consisting essentiallyof” the recited component(s).

When ranges are used herein, such as for dose ranges, combinations andsubcombinations of ranges (e.g., subranges within the disclosed range),specific embodiments therein are intended to be explicitly included.When the term “about” is used herein, in conjunction with a numericalvalue, it is understood that the value can be in a range of 95% of thevalue to 105% of the value, i.e. the value can be +/−5% of the statedvalue. For example, “about 1 kg” means from 0.95 kg to 1.05 kg.

A greater understanding of the embodiments of the subject invention andof their many advantages may be had from the following examples, givenby way of illustration. The following examples are illustrative of someof the methods, applications, embodiments, and variants of the presentinvention. They are, of course, not to be considered as limiting theinvention. Numerous changes and modifications can be made with respectto embodiments of the invention.

Example 1

The three-step process as shown in FIG. 1 was performed to prepare UHTCfoams of TaC, HfC, and TaC-HfC, with the three steps being UHTC slurrypreparation, freeze-drying, and SPS.

For each UHTC foam (TaC, HfC, and TaC-HfC), the preparation method wasas follows. An aqueous slurry of UHTCs with 10 wt % loading wasprepared. A PAA dispersant with 6 wt % of UHTC loading was added toobtain well dissolved UHTC slurry. The solution/slurry was constantlystirred at room temperature for 5 h while maintaining the pH at 8throughout the process. The UHTC aqueous dispersion/slurry was pouredinto a graphite mold, frozen and subsequently sublimed in a freeze dryerfor 24 h to obtain a green body. The green body was sintered bycalibrating a conventional spark plasma sintering (SPS) setup. The greenbody was kept inside a graphite crucible, and this whole assembly wasput inside the graphite die. The working space remained constant betweenthe punches of the SPS setup by not touching the sample/green bodyinside the standard graphite die, resulting in zero external pressure.The SPS parameters were configured for pressure-less sintering at 1850°C. for 10 min to give the UHTC foam.

FIGS. 2(a), 2(b), and 2(c) show the fabricated UHTC foams for TaC, HfC,and TaC-HfC, respectively. The dimensions listed in FIGS. 2(a), 2(b),and 2(c) show the dimensions of the as-fabricated foams. FIGS. 3(a)-5(d)show scanning electron microscope (SEM) images of the UHTC foams, withFIGS. 3(a)-3(d) showing TaC foam, FIGS. 4(a)-4(d) showing HfC foam, andFIGS. 5(a)-5(d) showing TaC-HfC foam. Referring to FIGS. 3(a)-5(d), themicrostructure of the TaC, HfC, and TaC-HfC foams showed the presence ofmacro-pores, meso-pores, and micro-pores with directionality in porealignment during FD. The relative porosity in TaC, HfC, and TaC-HfCfoams was about 54%, about 55%, and about 48%, respectively. The EDSmapping to show the solid-solutioning in TaC-HfC foam is presented inFIGS. 6-10 .

FIG. 11 shows the X-ray diffraction (XRD) analysis of the TaC-HfC foam,which further confirms the partial solid-solutioning in TaC-HfC foamduring the pressure-less SPS process. FIGS. 12-14 show the positioncontrol high load indentation for the TaC, HfC, and TaC-HfC foams,respectively, to predict the strength of these foams based on loadbearing ability against crack growth. The results showed that partialsolid-solutioning in the UHTC foams leads to better mechanical integrityin the TaC-HfC foam as compared to the parent UHTC foams (TaC and HfC).The load-bearing capacity was observed to be highest for TaC foam (about120 N). This is due to bigger macro-pores (˜40-80 μm) in the material,which during indentation leads to early cracking but at the same timecompacting the pore walls (struts), leading to pore closure at a fasterrate. However, in the case of HfC foam, the relatively highdensification of the struts and smaller macro-pores (<50 μm), instead ofcompaction cracking of struts, is more prominent, diminishing its load.The densified regions (dense struts) are more pronounced in HfC foamthan TaC (see FIGS. 3(a)-4(d)). The macro-pores in TaC-HfC arecomparable to that of HfC foam. Still, due to partial solid-solutioning,there is no evidence of cracking observed while maintaining moderateload-bearing (about 80 N) in the TaC-HfC foam.

FIG. 15 shows the thermal conductivity of the TaC, HfC, and TaC-HfCfoams. Referring to FIG. 15 , the 5-fold decrease in the thermalconductivity of TaC-HfC foam as compared to TaC highlights the efficacyof solid-solutioning in providing thermal insulation. The thermalconductivity of HfC foam is similar to that of TaC-HfC foam, but thelower load-bearing capability of HfC foam (cracking marked in FIG. 13 )makes TaC-HfC foam better than parent UHTC foams (e.g., TaC and HfCfoams).

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

All patents, patent applications, provisional applications, andpublications referred to or cited herein are incorporated by referencein their entirety, including all figures and tables, to the extent theyare not inconsistent with the explicit teachings of this specification.

What is claimed is:
 1. An ultra-high temperature carbide (UHTC) foam,comprising macro-pores, meso-pores, and micro-pores, the UHTC foamcomprising a porosity of at least 30%.
 2. The UHTC foam according toclaim 1, comprising at least one of tantalum carbide (TaC) and hafniumcarbide (HfC).
 3. The UHTC foam according to claim 2, the UHTC foambeing a one-component foam comprising TaC.
 4. The UHTC foam according toclaim 2, the UHTC foam being a one-component foam comprising HfC.
 5. TheUHTC foam according to claim 2, comprising TaC and HfC.
 6. The UHTC foamaccording to claim 1, the UHTC foam having a thermal conductivity ofless than 60 Watts per meter per Kelvin (W/m-K).
 7. The UHTC foamaccording to claim 1, comprising a solid solution of TaC and HfC.
 8. TheUHTC foam according to claim 1, the thermal conductivity of the UHTCfoam being less than 10 W/m-K.
 9. The UHTC foam according to claim 1,the porosity of the UHTC foam being at least 40%.
 10. The UHTC foamaccording to claim 1, the porosity of the UHTC foam being at least 50%.11. The UHTC foam according to claim 1, the porosity of the UHTC foambeing at least 55%.
 12. An ultra-high temperature carbide (UHTC) foam,comprising macro-pores, meso-pores, and micro-pores, the UHTC foamhaving a thermal conductivity of less than 60 Watts per meter per Kelvin(W/m-K).
 13. The UHTC foam according to claim 12, comprising at leastone of tantalum carbide (TaC) and hafnium carbide (HfC).
 14. The UHTCfoam according to claim 13, the UHTC foam being a one-component foamcomprising TaC.
 15. The UHTC foam according to claim 13, the UHTC foambeing a one-component foam comprising HfC.
 16. The UHTC foam accordingto claim 13, comprising TaC and HfC.
 17. The UHTC foam according toclaim 12, comprising a solid solution of TaC and HfC.
 18. The UHTC foamaccording to claim 12, the thermal conductivity of the UHTC foam beingless than 20 W/m-K.
 19. The UHTC foam according to claim 12, the thermalconductivity of the UHTC foam being less than 10 W/m-K.
 20. Anultra-high temperature carbide (UHTC) foam, comprising macro-pores,meso-pores, and micro-pores, the UHTC foam comprising a solid solutionof TaC and HfC, the UHTC foam comprising a porosity of at least 40%, andthe UHTC foam having a thermal conductivity of less than 10 Watts permeter per Kelvin (W/m-K).